Quasi-Periodic Pulsations during the Impulsive and Decay phases of an X-class Flare

TL;DR

This study investigates the characteristics and origins of quasi-periodic pulsations in X-ray emissions during an X-class solar flare, revealing multiple timescales and potential MHD processes involved in their persistence.

Contribution

It provides a detailed multi-wavelength analysis of QPP during different flare phases, highlighting their temporal behavior and possible physical mechanisms.

Findings

Identified characteristic timescales of ~20s and ~55s in flare emissions.

Persistent thermal pulsations observed up to 20 minutes into decay phase.

Suggests MHD processes like sausage or kink modes as drivers of decay phase pulsations.

Abstract

Quasi-periodic pulsations (QPP) are often observed in X-ray emission from solar flares. To date, it is unclear what their physical origins are. Here, we present a multi-instrument investigation of the nature of QPP during the impulsive and decay phases of the X1.0 flare of 28 October 2013. We focus on the character of the fine structure pulsations evident in the soft X-ray time derivatives and compare this variability with structure across multiple wavelengths including hard X-ray and microwave emission. We find that during the impulsive phase of the flare, high correlations between pulsations in the thermal and non-thermal emissions are seen. A characteristic timescale of ~20s is observed in all channels and a second timescale of ~55s is observed in the non-thermal emissions. Soft X-ray pulsations are seen to persist into the decay phase of this flare, up to 20 minutes after the non-thermal emission has ceased. We find that these decay phase thermal pulsations have very small amplitude and show an increase in characteristic timescale from ~40s up to ~70s. We interpret the bursty nature of the co-existing multi-wavelength QPP during the impulsive phase in terms of episodic particle acceleration and plasma heating. The persistent thermal decay phase QPP are most likely connected with compressive MHD processes in the post-flare loops such as the fast sausage mode or the vertical kink mode.